1. Field of the Invention
The present invention relates to an electric parking brake device and particularly, to an electric parking brake device wherein a parking lever for bringing brake linings of brake shoes into friction engagements with a brake drum is pivotally moved by an electric motor.
2. Discussion of the Related Art
For example, JP2009-092092 A (equivalent of US 2010/0206677 A1) describes the following electric parking brake device. In the electric parking brake device, a pushing device for pushing brake shoes to press brake linings on a brake drum is provided in the vicinity of an anchor block supporting respective one ends of the brake shoes. The pushing device is composed of an electric motor, a worm, a worm wheel, a screw member and a shoe pushing rod. The motor is fixed with a main body of the motor protruding on a vehicle body side relative to a back plate (backing plate) and with an output shaft of the motor protruding on a brake drum side through a through hole formed in the back plate. The worm is fitted on the output shaft of the motor. The screw member is bodily held on an inner circumference side of the warm wheel through a key.
A female screw is formed on the inner circumferential side of the screw member, while a male screw screw-engaged with the female screw of the screw member is formed on the outer circumferential side of the shoe pushing rod. Then, the shoe pushing rod is held to be relatively movable in the axial direction relative to the screw member. End portions of the shoe pushing rod are put between the brake shoes, and the shoe pushing rod is prevented from rotation about the axis thereof. The screw member is held to be relatively rotatable relative to a housing through bearings. In the electric parking brake device, the rotational motion of the motor is converted into the linear motion to move the shoe pushing rod in the axial direction, whereby the brake shoes are pushed to bring the brake linings into friction engagements with the brake drum.
In the electric parking brake device described in the Japanese application, the main body of the motor is fixed to project into the vehicle body side beyond the back plate. Therefore, the motor is exposed to the outside of the brake drum, which is not preferable in light of waterproof and dustproof. Further, for example, JP2011-099458 A describes the following electric parking brake device. The electric parking brake device is provided with an expansion/contraction device that widens the brake shoes to push the brake linings on the brake drum, and an electric motor for driving the expansion/contraction device. The motor is fixed to project into the vehicle body side beyond a back plate and is covered with a cover. Thus, the waterproof and the dustproof of the motor can be ensured.
In the electric parking brake devices described in the aforementioned Japanese applications, because the motor is fixed to project largely into the vehicle body side, it is feared that the motor interferes with hub components on the vehicle body side. In order to solve the problem, the motor suffices to be housed in the interior of the brake drum. However, a motor housing space in the interior of the brake drum is restrained, because it is necessary to avoid the interferences of the motor with the anchor block and the hub components on the vehicle body side. Further, the motor that outputs a power depending on the vehicle weight tends to increase in dimension and thus, it may be the case that the motor cannot be housed in the interior of the brake drum. Although if the brake drum were increased in dimension, the motor could be housed in the interior of the brake drum, there would arise a problem that restrains models of vehicles to which such a brake drum is attachable.